The main texture of dolomite of Middle Permian,western Sichuan basin:Concurrently on the differences with Upper Permian-Triassic,Northeast Sichuan basin
四川盆地西部中二叠统白云岩/石的主要结构类型——兼论其与川东北上二叠统—三叠系白云岩/石的差异

The dolomite texture is significant in the study of dolomite genesis. The textures of Middle Permian Qixia dolomite in western Sichuan basin are different from those of Upper Permian-Triassic dolomite in northeastern Sichuan basin. Besides the dolomite with porphyrotopic crystals, the Qixia dolomite, as a whole, is lack of fabric-preserving textures, but characterized by coarser non-planar anhedral to euhedral saddle-like dolomite crystals. However, the fabric-preserving dolomites are well developed in Upper Permian-Triassic carbonates in northeastern Sichuan basin, including predominantly finer planar euhedral to subhedral dolomite crystals. The distribution model of dolomite content of Qixia Formation in western Sichuan basin could be regard as a non-classical one, because the transitional rock type of 40% to 60% dolomite content is dominant; whereas the model of Changxing Formation of Upper Permian-Triassic dolomite in northeastern Sichuan basin could be seen as a classical one that has two dominant end-member rock types of more than 90% or less than 10% dolomite content respectively. The different dolomite textures could reflect the Qixia dolomite experienced the higher crystallization temperature, the lower Mg/Ca ratio of fluids and the shorter duration and incomplete halfway back dolomitization. In contrast, the Upper Permian-Triassic dolomite in northeastern Sichuan basin underwent the complete dolomitization with lower temperatures and marine-derived fluids of high Mg/Ca ratio.